So-called touchscreens having a touch-sensitive surface have become established in recent times as input or operator control elements in the most diverse application areas, in particular also in medical application fields. The success of touchscreens in medical engineering is due in particular to the fact that the surface of a touchscreen as a smooth surface compared to the individual keys of a keyboard is significantly easier to clean and accordingly the hygiene requirements for medical equipment can be more effectively satisfied. Accordingly, increasing use is now being made, in particular in medical application areas, of devices in which the control operations are performed almost exclusively via a touchscreen and only individual switches are present for activating the overall apparatus.
Touchscreens in state-of-the-art implementations typically consist of a TFT display and a superimposed touch-sensitive film covering the display. Touching the film causes a change in an electric field. By evaluating said change it can be established at which point the film was touched. By an appropriate interaction between display and film it is then ensured that information shown on the display can be activated or selected by touching the corresponding point of the film.
However, due to variations in the signals and possible signs of aging in the electrodes used for generating the electric field, a certain discrepancy can arise over time between the touch-sensitive film and the display, as a result of which the operation of the touchscreen is made more difficult. In the worst case operation of the touchscreen can be made totally impossible thereby, because the keys shown on the display no longer coincide with the corresponding areas of the film or the film key areas come to lie completely outside the screen. In order to avoid or rectify this, a calibration or an adjustment of the touchscreen is required in which a calibration is performed by means of a specific touching of the film and evaluation of the signals being generated in the process, with the result that ultimately agreement is once again restored between what is shown on the display and the position calculated on the basis of the resulting signals when the screen is touched.
Touchscreens are normally shipped together with an adjustment program which allows a calibration to be performed in the above-described way. Said adjustment program is usually launched via a keyboard or a mouse connected to the device which enables said adjustment program to be easily invoked.
However, medical equipment is—as was already mentioned above—routinely shipped with as few separate input and operator control elements as possible, with the result that only the touchscreen as input element and a central on/off switch for the device are available to the end customer himself. Thus, only the touchscreen itself can be used to operate the medical device at the end customer site. However, if said touchscreen is decalibrated, there is the risk that no more functions at all can be activated, since due to the decalibration the operator control elements can no longer be correctly registered and accessed. In such a case the touchscreen would be totally unusable and would have to be sent back to the manufacturer for recalibration. Alternatively thereto it would also be possible to provide an additional input device such as a mouse or keyboard, a situation which should, however, be avoided due to the above-cited hygienic disadvantages of input devices of said kind.